If someone tells you something with an expectation that you won't tell anyone else, it's a betrayal if you do.
The problem is that people associate "betrayal" with not being a good thing, when it's actually a neutral term.
But isn't that more about expectations? The confessor expects his listener to not reveal what's discussed. That's not always a reasonable expectation. There are protections in place for certain scenarios, like doctor-patient, attorney-client, parishoner-priest, etc.
If a friend confesses to you, you're not actually duty-bound unless you impose that constraint upon yourself.
In this case, even if Snowden signed a Non-Disclosure Agreement, I don't think he should be found guilty of violating it because what he was revealing was against the law (for the sake of this example). If you work for a bank, sign an NDA, and then blow the whistle on money laundering for drug cartels, which party should be prosecuted? I don't think the employee should be prosecuted. I think the bank managers who approved the laundering should be, and the corporation itself should be put to death
